Launching unmanned aerial vehicles (UAVs) from a submarine whilst the submarine is submerged poses a difficult problem. Conventional launch solutions that might be used on land or on ships are not suitable for use on submarines because they are designed to launch UAVs into clear air, not through a layer of water. Furthermore, UAVs are not typically designed for travel through water and could be damaged if launched into water.
Systems for launching UAVs from a submarine are currently in development. The first of these, Gabler's VOLANS system avoids the problem of launching through water by providing a dedicated submarine mast from which a UAV can be unfolded and launched using a catapult (the UAV hence being above the surface of the water on launch). However, this system requires a submarine to be heavily modified so as to carry the additional launch mast. It is also limited in that the submarine can be no deeper than periscope depth with the launch mast being required to break through the surface of the water in order to launch its UAV.
Raytheon Company of Waltham (Mass.), US, is also developing a UAV launch system for submarines, SOTHOC, which makes use of a submarine launch vehicle adapted for ejection from the garbage ejector of a submarine. The submarine launch vehicle carries the UAV to the surface by inflating a float collar and then makes use of a water drogue and vane to stabilise and align a launch tube at a 35 degree angle into the wind. The UAV is launched from the launch tube of the submarine launch vehicle by means of a conventional launch mechanism. Whilst the SOTHOC system allows a UAV to be launched while the submarine is submerged, the system suffers from the problems that many modern submarines do not have garbage ejector systems and the system is unreliable in rough seas. Furthermore, garbage ejector guns are reliant on the ability to drain down the water from inside the ejector to an internal waste water tank. If the tank is full or near to full then the internal waste water tank will have to be pumped overboard, which is a noisy procedure and might not therefore be possible if the submarine is to maintain a low acoustic signature. U.S. Pat. No. 7,946,241 discloses more detail of the floatable housing for deployment of an unmanned aerial vehicle adapted to be launched from a marine vessel.
A third system, the Lockheed Martin Cormorant, has previously been proposed at a conceptual level. The Cormorant was a 4-ton UAV having folding wings so as to allow it to fit into a Trident missile tube. In order to launch the Cormorant UAV, it was not fired from the tube but guided out on a “saddle” at a depth of 150 feet and left to float to the surface, during which time it unfolded its wings. The UAV's rockets were then used to lift the UAV away from the water surface and into flight. Due to its cost this project was not pursued.
There is therefore a need for improved apparatus for launching UAVs from a submarine.